Differential and RTK Corrections for the Internet Car

This paper describes new Differential and RTK GPS/GLONASS correction service through the Internet. The DGPS correction services that are available in Japan at present can not satisfy all potential users. Most of their limitations related to the fact that they use radio broadcast for their service. We will provide new correction services through the Internet using server and client models with propagation agents. The main advantages of our service are its flexibility and availability for every potential user. At present, we provide limited Differential and RTK service mostly for the test purposes and continue to develop related software. In this paper, we present the service concept, description and the results of experiments. 1. ADVANTAGE OF USING THE INTERNET FOR GPS/GLONASS CORRECTION SERVICES Currently, many types of GPS correction services are available in Japan. These services are depending on the radio broadcasting. Our new correction services will deliver Differential and RTK corrections through the Internet. There are several advantages of using the Internet as a propagation media for the GPS corrections. First, an infrastructure for such service will have low cost and at the same time, it will be easily accessible through the world. Second, licenses for radio broadcast will not be required for such service, which will also assist to utilize it worldwide. The other advantage is the possibility of bi-directional communication. In this case, a request from a user will be transferred to a reference station. The reference station will supply the user with the corrections that will be formed upon his request. These corrections will consist only of a subset of data, which help to decrease an amount of information we need to transfer through the Internet. 2. INTERNET CORRECTIONS PROPAGATION MODEL A model of our correction service is depicted on Figure 1. The model consists of three components that are connected through the Internet. A Reference Station generates corrections and sends this information to the Propagation Agents via the Internet. The Propagation Agents deliver the correction information to Mobile Clients. Upon the Mobile Client’s request, the Propagation Agent selects the correction information which more suitable for each Mobile Client. It also selects more suitable server for Mobile Client from the geographical and informational points of view. The Mobile Client receives the correction information from the Propagation Agents. The Mobile Client and The Propagation Agent communicate with each other. In a request message, the Client can include special request, such as a type of corrections (DGPS or RTK), or additional information, such as a preliminary location of the Client, that could be used by the Propagation Agent. 3. PROTOTYPE OF THE INTERNET CAR InternetCAR (a car with the Internet capabilities) is our first Mobile Client (see Figure 2). The InternetCAR accommodates a GPS receiver, BSD based Personal Computer, Wireless Network equipment and some other navigation sensors. A Reference Station has been constructed on Z-18 GPS Receiver, UNIX-based computer and Internet connectivity. The Reference Station is connected to the WIDE Internet Network Operation Center at KEIO University. This Network operates near the very core of the Japanese Internet, therefore, we can provide high quality GPS correction service for big number of users. 4. TEST RESULTS The results of the first experiments are depicted on Figures 4-10. Figure 4 shows two traces on a map of the Keio University. One trace belongs to a car equipped with a standalone GPS and another to the InternetCar. In this experiment, we supply the InternetCar with DGPS corrections through the Internet. Figure 5 and 6 compare the results of the standalone positioning and our DGPS service Reference Station Propagation Agents Mobile Clients Fig. 2 Prototype of the Internet Car. Fig. 1 Correction Information Propagation Model